This investigation focuses on neuroblastoma-associated antigens that are on neural differentiation molecules, on embryonic or fetal molecules or on polypeptides coded for by oncogenes. These molecules may contribute to the neoplastic phenotype and, because of their selective expression by tumor cells, may be useful targets for immunodiagnosis and immunotherapy. Recently developed biochemical methods for producing purified and defined immunogens are being used to make a new generation of monoclonal antibodies against gangliosides, polypeptides and oncogene products. These new antibodies and those produced previously are being used to investigate tumor heterogeneity and the relationship of antigen expression to the malignant phenotype. Immunodiagnostic studies aim to improve differential diagnosis, monitoring, prognostication, and identification of tumor cells in bone marrow. We shall complete studies that are demonstrating that the antigen phenotype correlates with prognosis and that immunoassays for tumor cells and serum antigen are sensitive and specific means of assessing tumor status. This investigation should contribute to a better understanding of neuroblastoma and to the development of new and improved diagnostic and therapeutic strategies.